Envelope structure for mercury pool rectifier tubes



Nov. 22, 1955 A. J. HUMPHREY 2,724,785

ENVELQPE STRUCTURE FOR MERCURY POOL RECTIFIER TUBES Filed Jan. 26, 1952 FIG|.2.

INVENTOR.

AJ. Humphrey 12. HIS fl TTOR N EY.

United States Patent ENVELOPE STRUCTURE FOR MERCURY POGL RECTEIER TUBES Andrew J. Humphrey, Cleveland, Ohio, assignor to Reliance Electric and Engineering Company, Cleveland, Ohio, a corporation of Ohio Application January 26, 1952, Serial No. 268,368

2 Claims. (Cl. 31329) This invention relates to gaseous discharge rectifier tubes of the mercury pool type, and more particularly to the envelope structure for an air-cooled tube.

In mercury pool rectifiers, mercury is evaporated rapidly from the surface of the cathode pool by heat at the cathode spot; and the mercury vapor thus produced tends to increase the vapor pressure and reduce the inverse voltage that will cause a breakdown and conduction in the wrong direction, and also the forward voltage rating for a control rectifier. In mercury pool rectifiers with which I am familiar, the desired low vapor pressure and resultant voltage ratings are obtained by water cooling the walls of a metal envelope, or providing a large condensation chamber for air-cooled glass envelopes, so as to have surfaces at a sufiiciently low temperature to condense the mercury vapor as rapidly as it is evaporated from the cathode pool. For many applications and uses of mercury pool rectifiers, it is desirable to avoid the complication of water cooling metal envelopes for dissipation of heat during operation of the tube; yet the glass envelopes for air-cooled rectifiers are awkward in size and shape on account of the large condensation chamber required for condensing the mercury vapor.

With these and other considerations in mind, the principal object of this invention is to provide an envelope structure for air-cooled mercury pool rectifiers, which has an acceptable conventional shape and size-for its current rating, and still provides the desired low vapor pressure for high voltage ratings.

Generally speaking, and without attempting to define the nature and scope of the invention, it is proposed to support the mercury pool cathode on a metal bottom of an air cooled glass envelope, and provide suflicient area and heat dissipating surface for such metal bottom to maintain at and around the cathode itself a region of low temperature for condensation of the mercury vapor at a rate to maintain the desired low vapor pressure, while heat of the discharge is dissipated from the anode and other parts by radiation and conduction at higher level of temperature through the glass body of the air cooled envelope, thereby obtaining an air-cooled mercury pool rectifier of simple shape and moderate size forits current rating.

Various other objects, characteristic features, attributes and advantages of an envelope structure of this invention will be in part apparent, and in part pointed out as the description progresses.

Although this invention may be embodied in various types and forms of mercurypool rectifier tubes, it is convenient in describing the nature of the invention and its characteristic features to refer to a tangible physical embodiment of the invention, such as the typical structure illustrated in the accompanying drawings.

In these drawings,

Fig. 1 is a general view of a typical envelope structure embodying the invention, with a diagrammatic representation of a typical arrangement of electrode and shielding structures for a tube of this type.

2,724,785 Patented Nov. 22, 1955 Fig. .2 .isa fragmentary view of a portion of the preformedstrip from which the'radiator is preferably made.

Fig. 3 is a View ofa small arcuate part of the radiator formed by bending a strip of Fig. 2 into a circle; and

Fig. 4 .is a cross section through the radiator taken on a radial crosssection line through the base of the tube, such as indicatedby 4--4 in Fig. 3.

The gaseous discharge rectifier of the mercury pool type :to which :this :invention relates employs a pool of mercury as .a cathode, together with suitable means for initiating an arc :discharge .to the anode by an igniter .element, or maintaining'a keep-alive arc discharge to be transferred .to the main anode, subject to the controlling eifectof-a grid, all in a manner familiar to those skilled inthe art. In general, any suitable structure and arrangement ofaelectrodes maybe employed to advantage in the envelope structure .of this invention; and the arrangement of parts diagrammatically represented in Fig. 1 for explanatory purposes is merely typical.

The 'tube elements schematically shown in Fig. 1 for the purpose of explanation comprise in general an anode A, a control grid G,.an anode shield S with an arrangement of baffle plates, and a keep-alive anode KA, these parts being assumed to .be constructed and supported with the appropriate lead-in connections in a glass .tube envelope E inaccordance with the disclosure of the application ofWilliam P. Kruger, Ser. No. 268,390, filed January 26, 1952. In this structural organization assumed, the anode A, preferably a block of carbon, is attached to an anode supporting lead 2 sealed in the upper .end of the glass envelope E, which in accordance with. this invention may conveniently have the conventional cylindrical shape. The anode supporting lead 2 is attached 'toa mp3 of the appropriate metal capable of forming a gas tight seal with the glass used for the envelope, such as .theaalloy commonly known as Kovar; and a glassato-metal seal is formed in the usual way between the periphery of this cup 3 and a re-entrant neck 4 of the envelope E. The external conductor 5 connected with theanode is attached to the cup 3. A metal sleeve 6 with its upper end fitting inside the peripheral flange of the-cup 3 surrounds the anode lead 2. The shield S, having baflle plates 8 below the grid G, is shaped to have a close, short-path spacing to all surfaces of the anode A and its sleeve 6, except for an area opposite the grid G; and the upper end of this shield S sets in a packing 9 of quartz wool'o-r the like within the re-entrant neck 4 of the'tube envelope, in the manner and for the purposes disclosed and claimed in the application of W. P. Kruger above mentioned. This arrangement of parts schematically illustrated and briefly described represents a typicalstructural organization of tube elements for a grid control tube .ofathe mercury pool type adaptable for use with the envelope structure of this invention.

in accordance with this invention, the lower open end of the glass envelope E is-closed by a circular metal base or bottom B, upon which the mercury cathode pool indicated at 10 is supported. This base B is sealed to the lower edge of the glass envelope E, preferably by making this base of a metal, such as commonly known as Kovar, capable of forming a gas-tight seal with the glass, and forming this base with a circumferential groove or trough to receive the glass, in accordance with the disclosure of the William P. Kruger application above mentioned.

A radiator, designated as'a whole R, is attached to the metal base B to facilitate heat dissipation by affording extensive surfaces exposed to the air passing over these surfaces by natural or forced circulation. This radiator is preferably formed of a single strip 12 of a resilient metal of good heat conductivity, such as copper, which is folded or pleated transversely, as indicated in Fig. 2, with sharp bends along one edge, so that the strip thus pre-formed may be readily bent into a circular radiator to fit circular base B. An arcuate portion of this strip 12 when bent to form a complete circle is shown in the fragmentary view of Fig. 3. The individual crimps or folds of this pre-formed strip 12 when bent into a circle, are attached along one edge by fused metal, such as by a brazing or soldering operation, to the underside of the base B, as indicated at 13. The strip 12 after being pleated is cut away along one edge as indicated at 15 to give each pleat or fold a cross section such as shown in Fig. 4. Also, the curvature of the transverse bends in the strip 12 is preferably selected to give approximately equal spacings between opposing surfaces of the folds or pleats of this strip when it is bent into a circle and attached to the base B. A suitable fan or blower (not shown) is preferably used to force air through a suitable duct as indicated at 16 against the bottom of the radiator R.

This structure of the radiator R affords extensive exposed surfaces for heat dissipation in a limited space, and may be readily fabricated. The inherent resiliency of the strip 12 causes its folds to assume substantially equally spaced positions extending radially of the base,

when the pro-formed strip is bent into a circle. The cross section of the strip 12 may be selected to afford the desired area for the heat radiating surfaces of the radiator R as a whole. The external circuit connector (not shown) for the cathode is conveniently attached to this radiator R.

In accordance with this invention, mercury evaporated from the cathode pool during operation is condensed at and around the cathode itself, rather than in a separate condensation chamber, by maintaining the cathode pool as a Whole, except of course the cathode spot, and to some extent the adjacent surfaces of the walls of the tube envelope, at a temperature level suitable for the desired mercury condensation. Referring to the embodiment of the invention illustrated, the cathode pool indicated at 10 is a relatively thin layer of mercury over a substantial area of the relatively thin metal bottom B. This permits conduction of heat from the cathode pool to the outside of the tube envelope at a relatively low temperature gradient. The heat conducted through the metal bottom B can be readily dissipated by air cooling of a properly proportioned radiator R to keep a region at and around the cathode pool at a temperature low enough for mercury condensation. The movement of the cathode spot and agitation of the mercury characteristic of mercury pool tubes tends to distribute the cathode heat and facilitate its dissipation through the metal body of the tube envelope. In this connection, the metal base B and also the mercury itself are good conductors of heat, as compared with the walls of a glass envelope, so that the area required for heat dissipation by air cooling to maintain the cathode at a temperature suitable for mercury condensation is much smaller than the area for mercury condensation on glass walls, so that a tube envelope of moderate size and conventional cylindrical shape may be employed for a tube of a given current rating.

When the tube is conducting current, the anode A, shield S and associated parts, together with the vapor of the surrounding plasma tend to assume an elevated temperature. The general level of the vapor pressure, however, which dictates the voltage rating for the tube, is primarily determined by the temperature of the coolest part of the envelope, i. e. the region at and around the cathode pool. In other words, the anode and shield in the upper part of the tube envelope may assume a high level of temperature in operation, while the vapor pressure determining the voltage rating for the tube is maintained at the desired level by air cooling the radiator R and metal base B. This elevated temperature of the anode, shield and associated parts during operation increases the efficiency of heat dissipation through the glass body of the tube envelope, due to the greater difference in temperature, so that an air cooled envelope of moderate size will afford the desired heat dissipation. In this connection, dissipation of heat from the shield S, for example, by radiation to the glass walls is a function of the fourth power of the difference in absolute temperature, and conduction of heat through these glass Walls to the air cooled exterior increases directly With the difference in temperature. Accordingly, in the tube envelope of this invention, the heat of the anode and the plasma in the upper part of the tube is efficiently dissipated at a high temperature level, while the desired vapor pressure is obtained by maintaining the cathode pool at a much lower temperature, so that the tube envelope with air cooling may be of conventional shape and small over-all dimensions for its current rating.

From the foregoing it can be seen that this invention enables an air-cooled envelope of conventional shape and smail size to be employed to advantage for mercury pool rectifier tubes.

What I claim is:

1. An air cooled mercury pool rectifier tube comprising, an envelope having a glass body sealed to the periphery of a circular metal bottom member, said metal bottom member supporting a thin layer of mercury Within the tube to constitute the cathode, and supporting outside the tube a radiator comprising a single strip of resilient metal bent in a series of folds in the form of a circular ruffle having an outer circumference substantially the same as the circumference of said bottom member, the inner ends of said folds being sharp bends and the outer ends of said folds being rounded bends, said series of folds having their outer and upper corners cut away and their inner upper edges attached to said metal bottom member by fused metal, whereby the massed metal at the inner circumference of the ruffle formed by the ends of said folds causes a rapid conduction of heat away from said bottom member to the radiating metal folds having passages for the movement of convection air currents both radially and axially of the tube.

2. An air cooled mercury arc rectifier tube comprising, an evacuated envelope including a circular flat base of thin metal and a body sealed to the periphery of said base, said base supporting a shallow pool of mercury constituting the cathode of the tube, and an air cooled radiator directly attached to the outer bottom surface of said base for dissipating heat from the cathode pool as a whole, said radiator comprising a member of thin and closely spaced metal strips of good heat conductivity distributed over the outer bottom surface of the base, said metal strips being edgewise to said outer surface and having their inner edges directly attached to said outer surface of the bottom of said base, and said metal strips forming passages permitting air flow radially and axially of the tube.

References Cited in the file of this patent UNITED STATES PATENTS 

